1. Field of the Invention
This invention relates to an anchor bolt assembly. More particularly, the invention relates to an anchor bolt assembly useful in bore holes containing a settable bonding material. Such assemblies are useful in anchoring heavy machinery, in construction applications, and mine roof supports.
2. Description of Related Art
It is well known in the art of mine roof support and related anchoring systems to tension bolts by the use of the mechanical expansion system in combination with a settable bonding material. The popular bonding materials are provided in compartmented packages in which a resin and a catalyst for the resin are separated. Such a system is disclosed in U.S. Pat. No. 4,280,943. Proper mixing of the catalyst and resin as well as final tensioning of the anchor bolts have been problems. Mixing must take place within seconds and final tensioning within a very few minutes.
Anchor bolts having various profiled configurations have been used to promote mixing. Illustrative of this type of anchoring device is that shown in U.S. Pat. No. 4,393,638. A tapered bolt having grooves and ridges having a spiral configuration is said to promote mixing of the resin and force it into the inner end of the bore. A bolt having a helical channel adjacent the end is shown in U.S. Pat. No. 4,564,315. Such devices require machining or forming and are somewhat costly to manufacture.
Tensioning of the bolts has been achieved using various bolt and expansion shell configurations. Bolt and shell combinations of the type shown in U.S. Pat. No. 4,413,930, depend on tensioning by advancing a camming plug which is threaded onto the bolt through an anchoring shell. Expanding fingers on the shell grip the bore wall holding it in place while it is placed under tension. Such mechanical devices, although effective in tensioning the bolt, create highly concentrated loading on the walls of the bore hole which can crack the walls.